This invention relates to pressure vessels and, more particularly, to a seal arrangement between separable container sections which is adapted to relieve pressure if the container sections are improperly assembled or if the operating pressure of the vessel is exceeded.
Pressure vessels which are employed as swimming pool filters generally may be categorized as separable and non-separable. Non-separable pressure vessels contain a filter medium such as sand, which may be cleaned by backwashing techniques to condition the medium for further filtering operations. Access to the interior of the pressure vessel is not necessary, since the medium and even the filter laterals may be removed through a relatively small access opening.
Separable pressure vessels are needed for filtering techniques that require internal access for manufacturing and service maintenance throughout the life of the filter. Filtering arrangements in this category are diatomaceous earth, cartridge, and stacked disc filter arrangements.
Historically, the design of a separable tank has endeavored to follow the same design principles as a non-separable tank without distinction. This involves designing with conservative safety factors for strength and a requirement for leak integrity that is comfortably above the design working pressure. This is to ensure that the product is reasonably safe to use over extended time and exposure to environmental conditions. In defining tank seals, therefore, the tendency has been to make the seal fail-safe to such a degree that the seal maintains its integrity up to the structural limits of the tank side wall or the mechanical clamp holding the sections together. The conservative design of such tanks assumes that the tank will be correctly operated and assembled according to its design specifications. Frequently, however, the end user of the tank will ignore the manufacturer's assembly instructions and operating requirements, resulting in hazardous conditions. Thus, if the tank is improperly assembled after filter maintenance or replacement, the seal will maintain a leakproof condition, while the improperly assembled clamping band will be stressed beyond its mechanical capabilities even under normal operating pressure conditions. On the other hand, if the tank is properly reassembled and the user subjects the tank to abnormally high internal pressures by, for example, connecting the tank directly to city water pressures, the seal may maintain its integrity up to the burst pressure of the pressure vessel. These conditions are exacerbated if air is trapped in the vessel.
Conventional and logical approaches to relieving excess internal tank pressure by providing pressure relief valves to not solve the problem, since pressure relief valves are not adequately sized to handle the tremendous volume of fluid required to return overpressurized tanks to a safe condition, particularly if air is trapped in the tank. Moreover, excess operating pressures may not be encountered if the mechanical clamping band is improperly installed, thus creating a condition where normal operating pressures may place undue stress on the band.
The hazard posed by the separable pressure vessel is particularly dangerous in that it may occur without warning. If a separable tank is improperly assembled or overpressurized, the container sections may separate violently or rupture violently, respectively.